Previously known acoustic (audible and ultrasonic) position measurement techniques propagate acoustic pulses or bursts, the leading edges of which are detected and in turn provide time-of-flight information from which the distances from the pulse transmitters are calculated. However, such techniques yield poor rejection of interference from external noise and thus low accuracy.
Measurement and location in 3-dimensions requires measurement from at least three points spaced apart in or near the volume of a region in which the location is to be determined. The three (or more) measurements are usually taken sequentially, where the time for each measurement is sufficient for the pulse to propagate along the maximum distance from the transmitter to the receiver, thus seeking to avoid ambiguity in measurement from simultaneously detected leading edges of the signals. In applications where the operating distances between the transmitters and receiver(s) are 3 meters, the time-of-flight is about 10 milliseconds, which for a minimum of three measurements per point, results in a maximum position update rate of 33 times per second, too low for many applications. Applications requiring simultaneous tracking of dozens of points from sequentially activated transmitters, such as for full body motion capture in virtual environments, typically fail the requirement for line-of-sight paths between transmitters and receivers because portions of the body eclipse the paths. However, adding transmitters to reduce the line-of-sight limitations also adds to the time used to detect, measure, or calculate the three-dimension point locations, further reducing the update rate.